Preheat oven to 375 degrees.Toss the potatoes, cream, rosemary, garlic and salt and pepper together in a large bowl. Empty into a casserole dish (potatoes should be 2-3 inches high in the dish). Top with crumbled goat cheese. Bake for about 40 minutes or until potatoes are fork-tender. Remove and let cool for 20 minutes before serving (don't skip this step or your gratin will be too runny!!).